fix(macos): tests fail to build with latest Xcode

[tido64]

Description

macOS tests fail to build with latest Xcode:

/~/ios/ExampleTests/ManifestTests.swift:15:13: error: cannot find 'XCTFail' in scope
            XCTFail("Failed to read 'app.json'")
            ^~~~~~~
/~/ios/ExampleTests/ManifestTests.swift:19:9: error: cannot find 'XCTAssertEqual' in scope
        XCTAssertEqual(checksum.count, 64)
        ^~~~~~~~~~~~~~

Platforms affected

• Android
• iOS
• macOS
• Windows

Test plan

1. Should build successfully with latest Xcode:

   cd example
   pod install --project-directory=macos
   ../scripts/xcodebuild.sh macos/Example.xcworkspace build-for-testing
   

2. We should not overwrite existing setting. The following should fail the build:

   diff --git a/example/Example-Tests.podspec b/example/Example-Tests.podspec
   index f504e44..6b65a70 100644
   --- a/example/Example-Tests.podspec
   +++ b/example/Example-Tests.podspec
   @@ -18,6 +18,7 @@ Pod::Spec.new do |s|
      s.dependency 'ReactTestApp-DevSupport'
   
      s.framework             = 'XCTest'
   +  s.pod_target_xcconfig   = { 'ENABLE_TESTING_SEARCH_PATHS' => 'NO' }
      s.user_target_xcconfig  = { 'ALWAYS_EMBED_SWIFT_STANDARD_LIBRARIES' => '$(inherited)' }
   
      s.source_files = 'ios/ExampleTests/**/*.{m,swift}'